well, that's be kings parks job since kings had hanna barbera
"had" being the key word. Not sure who, if anyone, has the rights in North America right now.
Also remember that companies can have agreements and rights while others have rights to some too (and this could be done a multitude of ways such as a company having the rights and agreeing to let other companies have said rights dependent on use and territories). A company can pay a pretty penny for exclusivity but if it doesn't really affect their market, an agreement could also work.
A few important moments in history regarding this:
-While Kings Entertainment had the rights to Hanna Barbera, Universal did as well.
-When Knotts Camp Snoopy lost rights to PEANUTS after Cedar Fair lost the management contract, they went on to convert into Nickelodeon Universe (which it is still today, after a brief time being the "Park at MoA"). Paramount Parks had just been sold to Cedar Fair two years prior to this opening as Nickelodeon Universe. Paramount owned Nickelodeon and let Cedar Fair continue the use of Nickelodeon through 2009 while Nickelodeon Universe was operating. In addition, Universal also had rights to utilize Nickelodeon characters in attractions (Jimmy Neutron's NickToon Blast) and parades.
-Marvel is a big example though the rights for amusement attractions in Florida were sold back when Marvel was really at an almost point of no return and needed the influx of cash. This was well before Disney purchased the company. Universal has the rights to Marvel characters such as Spider-Man, X-Men, Hulk, etc... but only the comic versions and they cannot be related to the present MCU. Disney can introduce other Marvel characters to their Florida parks (see Guardians of the Galaxy) but cannot introduce the ones above (which is why you see a Spider-Man attraction in California for Disney but not Florida).
Probably the biggest one to note in relation to this discussion is that Six Flags doesn't have exclusive rights for Warner Bros/DC Comics/Looney Tunes. They do in most states and territories but the latest agreement left out Florida. So, realistically, Universal could approach Warner Bros for the rights in Florida and could build a park section or attraction based on DC Comics or Looney Tunes. Now, Warner Bros is in the process of being sold to Paramount Skydance so who knows how they will negotiate here but, in the past, they have been pretty willing to negotiate.
While I'm not sure it would actually happen, it is totally possible that Warner Bros could bring both Enchanted and Six to the table and discuss the use of rights. SIX has pretty much exited all of the markets where these sales took place (with the exception of potentially Michigan being an argument because there will be heavy marketing there still with Cedar Point, Great America, and Kings Island being close by). It may also lower the fee potentially for SIX while also offering more of an influx for WB. Not saying it will happen, but it is entirely plausible and the fact that Enchanted Parks has already begun negotiations with them is a sign that they're potentially willing. I'd even bet that PEANUTS could potentially be on the table. The new combined chain isn't entirely sure where they want to go with the rights and theming and who knows where they will be five years down the road with it too (with Peanuts expiring prior to that).
